Long term post-tetanic facilitation of responses of the sympathetic ganglion following repetitive preganglionic nerve stimulation is being studied as part of a broad investigation of prolonged trans-synaptic influences of nerve activity. The changes in responsiveness of nicotinic and muscarinic receptors following repetitive nerve activity will be studied, and the effect of altering acetylcholine metabolism, catecholamine metabolism, energy metabolism and protein synthesis on these responses determined. The major part of the investigation will be done using the rabbit superior cervical ganglion preparation in vitro with a sucrose gap recording technique. The depolarizing effects of a typical nicotinic stimulant and a typical muscarinic stimulant on the ganglion before and after repetitive preganglionic nerve stimulation will be studied. The effects of altering nerve and metabolic activity on their responses will be determined. Intracellular recording from single surface rabbit ganglion neurones will be used to see if repetitive preganglionic nerve activity causes changes in electrical constants of the neuronal membrane which could be related to the time course of facilitation. Post-tetanic facilitation may be an important mechanism for modulating ganglionic activity during intense reflex activity or for the development of tolerance to certain cardiovascular drugs.